Force direction in manual wheel chair propulsion: balance between effect and cost.

OBJECTIVE To evaluate the relationship between mechanical effect and musculoskeletal cost in wheelchair propulsion. DESIGN Simulation of force direction, based on experimental data from wheelchair users. METHODS For nine wheelchair users driving at 20 W, 1.39 m/s, the force direction was compared to simulation results based on a criterion defined as the ratio of mechanical effect and musculoskeletal cost. RESULTS Simulation data compare well to the actual force direction for the middle and final parts of the push. CONCLUSIONS The musculoskeletal cost of the exerted force must be taken into account to explain the observed propulsion pattern. Experienced users appear to optimize the force pattern by balancing mechanical effect and musculoskeletal cost of the pushing action. RelevanceThe effect-cost ratio may be a useful tool in analysing and improving wheelchair design.